At present, further demanded for liquid crystal displays are lower power consumption, enhanced brightness, and an enlarged viewing angle. It is possible to enhance the brightness of a transmission type liquid crystal display by increasing the light amount of the backlight. However, problems result in which the power consumption increases, heat is generated, and the size of the liquid crystal displays increases. Another effective method to enhance the brightness is to arrange a brightness enhancing film (or a dual brightness enhancing film: DBEF) between the backlight and the polarizing plate, which is a widely employed means. Of light coming from the backlight side, the brightness enhancing film selectively transmits polarized light which transmits a polarizing plate, and the polarized light absorbed in the polarizing plate is selectively reflected and reused, whereby the brightness is enhanced due to decreased light amount which is absorbed by the polarizing plate.
At present, the polarizing plate, mainly employed in liquid crystal displays, is structured in such a manner that a polyvinyl alcohol film, serving as a polarizer, is adhered employing two sheets of triacetyl cellulose film (hereinafter referred to as TAC film). Features of the TAC film are high transparency, low retardation, and ease of adhesion to a polarizer. However, TAC film exhibits retardation specifically in the thickness direction. When the brightness enhancing film is employed, linear polarized light in the oblique direction is converted to elliptic polarized light via retardation in the thickness direction of the TAC film. Accordingly, brightness in the oblique direction is decreased due to light absorption in the polarizer. In Patent Document 1, problems of color shift are overcome by decreasing the retardation of the polarizing plate protective film via the similar constitution. However, this technique resulted in problems in which adhesion to the polarizer was insufficient due to the use of non-cellulose based thermoplastic resins, whereby the adhered polarizer easily peels off.
Further, the polarizing plate protective film on the backlight side is exposed to a high temperature to tend to result in variation and non-uniformity of the retardation, resulting in problems in which the uniformity of brightness tends to vary.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2004-271846